Beneficiation treatment of phosphate rock for preparation of fertilizers and other products



J. G. KRoNsr-:DER ETAL 3,518,072

June 30, 1970 BENEFICIATION TREATMENT OF PHOSPHATE ROCK FOR PREPARATION OF FERTILIZERS AND OTHER PRODUCTS `Filed Nov. f5, 1966 lll Alf/@fed United States Patent Office 3,518,072 BENEFICIATION TREATMENT OF PHOSPHATE ROCK FOR PREPARATION OF FERTILIZERS AND OTHER PRODUCTS John G. Kronseder, 27 Pumpkin Hill, and David W. Leyshon, 110 Cross Highway, both of Westport, Conn.

Filed Nov. 3, 1966, Ser. No. 591,728 Int. Cl. C05b 1/00, 17/00 U.S. Cl. 71-41 4 Claims ABSTRACT 0F THE DISCLOSURE Phosphate rock having a Cao/P205 ratio in excess of 1.50 is beneiiciated in a iluidized bed reactor having a plurality of superposed treatment zones to increase the BPL content and lower the Cao/P205 ratio of the rock.

Rock to be treated is initially preheated, calcined at a temperature of from 1200 to 1850 F. and cooled to from 600 to 1200 F. Thereafter, the thus cooled rock is treated with phosphoric acid having P205 content from to 40% to further cool the calcined rock to a temperature of from 220 to 550 F. and simultaneously beneciate the rock.

This invention relates to a process `for treating low grade phosphate rock for producing valuable products therefrom.

One advantage of this invention is to both upgrade the low grade phosphate yrock and cool it, subsequent to calcination treatment.

Increasing world demand for the preparation of fertilizers and other products utilizing phosphoric acid in their preparation has created a serious drain on the rapidly diminishing world sources of high grade phosphate rock. A necessary corollary and consequence of this has been the increased dependence by the manufacturer of phosphoric acid on the use of low grade phosphate rock.

These lower grades of phosphate rock must rst be thoroughly beneficiated in order to bring them up to processible grade before they can be subjected to acid |generating treatment.

As long as this added beneficiation can be performed within economical limits, these ores can be profitably utilized in phosphoric acid manufacture. The best of these low grade ores can usually be economically processed to about 72% BPL (bone phosphate of lime), which is a commodity recognized in international trade as a shipping grade rock. The marginal grades require more extensive treatment but in general the cost of beneciating these marginal grade rocks exceeds the value of the rock in the world markets.

One technique commonly employed to beneficiate phosphate rock is to subject the rock, which has been comminuted to proper size, to combustion or calcination treatment in a fluidized bed reactor to remove certain contaminants which interfere with the subsequent wet processing of the phosphate rock to phosphatic fertilizers.

After calcination, the phosphate rock is cooled so that it may be conveniently handled. This cooling is accomplished by spraying water directly on the rock. While this technique is effective for eliminating the organic contaminants in the rock it does not improve the percent BPL content of the rock.

Accordingly it is an object of this invention to combine calcination treatment of phosphate rock with a novel cooling operation so that the combined processes yield an improved product that has been upgraded as well as cooled.

Another object of this invention is to provide a process for producing high grade phosphate rock while eliminating 3,518,072 Patented June 30, 1970 losses of P205 and at the same time providing a more efficient, simple process with a minimum of steps at an economically feasible cost.

An important object of this invention is to produce a 75% `BPI rock, or better, starting with raw phosphate rock in the sixty-six to` seventy percent BPI range.

Another object of this invention is to eliminate sulphide sulphur present in the low grade-` rock so as to reduce corrosion in subsequent treatments.

It is another object of this invention to substantially reduce free calcium oxide and to provide a phosphate rock product with a CaO/P2O5 ratio of approximately 1.50 or less, preferably 1.35 to 1.45.

In the practice of this invention it has been surprisingly found that any conventional, low grade phosphate rock, preferably in the 60 to 70% BPI range, that is mined in the general range of -20 to +200 mesh (Tyler), or alternately can be first crushed and/or ground to produce a crushed rock in the general range of -20 to +200 mesh (Tyler) followed by calcination and subsequent cooling with phosphoric acid to yield a beneciated rock product high in P205 and relatively low in CaO content. This process results in an upgrading of the rock during the cooling process.

In an alternative process, according to another embodiment of this invention phosphoric acid may be added to and during a drying operation after all or a part of the water is evaporated from the rock so as to reduce calcium oxide/P205 ratio and upgrade the rock.

Any phosphate rock conventionally used Without regard of geographic origin for producing phosphoric acid, particularly including North Carolina and North African rock, both of which are high in calcium oxide, may be used in the practice of this invention. Western United States and middle east rock like that of Jordan are also high in CaO. Florida, Tennessee, Baja Mexico, California minerals, etc., may likewise be beneiiciated by this process of this invention.

Although the processes of this invention are primarily directed to any phosphate rock, particularly those from the sources indicated above, they are especially applicable and most beneiicial to those phosphate containing rocks that have a BP-L in the range of 616 to Of course, it will be readily apparent to one skilled in the art that this invention may be applied to any phosphate material including those materials that have a higher or lower BPL range.

This invention has particular application to phosphate rock containing lattice CO2 where CaCO3 substitutes for Ca3(PO4)2 in the rock. This type of CaO cannot be removed by conventional beneciation techniques.

Prior to calcining or drying the phosphate rock should be crushed or otherwise comminuted if not mined at the sizes indicated above to pass a 20 and is retained on a 200 mesh screen (Tyler series). In the next step the rock is preferably subjected to a calcination or high temperature roasting treatment as is conventional in the art. In the practice of this invention any conventional calciner or furnace may be used wherein a temperature of 1200 to l850 F. may be maintained so as to completely calcine or roast the nely divided or crushed phosphate rock for a period ranging from about ten minutes to two hours, as desired.

This invention will now be described by way of example with reference to the accompanying drawings in which:

FIG. 1 illustrates a three-stage iluidized bed calciner and cooler as one form of the apparatus that maybe used to practice the preferred embodiment of this invention. The three stages are a preheat or drying zone, a calcining zone and an air cooling zone.

FIG. 2 illustrates the application of the invention to a fluidized bed dryer.

Into an upright uid bed reactor 1 phosphate feed rock particles of the proper size, as indicated above, is fed into a drying or preheat zone 2 by means of a conduit or pipe 3. Preheated or dried solids are transferred, by gravity to calcining or roasting zone 4 by conduit 5. Fuel and air enter this preheat or drying fluid bed zone through conduits 8 and 7, respectively. Air that enters through line 7 ows up and through apertures 9 in support 10 to act as Cil from about 1 to 5 pounds of acid per hundred pounds of rock and by combining this step with the phosphoric acid cooling step described above, sulfide sulfur can be materially reduced in the final calcined product.

It is also preferred to spray the phosphoric acid, coolling agent into the cooler in a manner similar to the addition in the present cooling systems in use in the prior art. It is also preferred to use a closed cooling system as considerable quantities of the H3PO4 may be vaporized or evaporated by the sensible heat from the hot calcined l a iiuidizing gas, and the fuel burns in the presence of said phosphate mineral. If any phosphoric acid is evaporated ftftolinlg heatedhto a temperltlure in the rage o it rriaytbethcondelnsed in cgnventionll applaratus and reo in pre eat zone e comminu e roc cyc e o e coo er or to t e origina supp y so as to prooverflows into conduit and enters the intermediate fluidvide a cyclic system. Any drum, screw or conventional ized bed of calcining or roasting zone 4 where the rock 15 cooling apparatus or device as set forth above may be used particles are heated to a temperature ranging from about so :long as the final product temperature, i.e., the phos- 1200 to 18.50 F. The increased temperature may be phate rockand the phosphoric acid that is removed from riliaitntdairied irrzone 4 pasfing airi tllat has gein prei; thet cooler illat la; tmprhature high enough Ito rmove iill ea e in coo ing zone y ui e upwar roug wa er so u e 2 5. is temperature s ou usua y apertures 9 along with fuel that enters through line 6. This 20 be in the range of about 220 to 550 F. preheated air that enters zone `4 acts as the fluidizing gas This following example is presented as a mere illustrafor the fluid bed for the calcining of the rock particles and tion of the invention and is not intended as limitative for the burning of the fuel. Ambient or low temperature thereof: air is pumped into the reactor through line 13 and ows EXAMPLE if, a or aro ina p osp a e roc percent to arrastranfaitafisiirarifsi a of 76% e an at t e same time improving t e CaO/P2O5 ratio. tfansfefed by lgfattl/Tlondul 151601' other com ventlonal 30 One hundred parts by weight of this sixty-seven percent means 0 a C00 er C C00 el may COmPUSe a con' BPL, hos hate rock of North Carolina ori f d ventional rotary screw or uid bed or other cooler. A uid irrt@ alzhre Stage calciner as shown in FIG lgrlrI/ Xravgbed 0001er may be Preferred t0 aVOd high temperatures age size of -20 mesh and had the following analysis or fumes as an alternative to a rotary screw cooler or any (dry basis) p,rior to treatment: other cooler. Phosphoric acid in a concentration of to P205 r0 6 40 weight percent in a quantity ranging from 2 to 20 35 Cao 4&3 pounds per 100 pounds of rock particles is pumped into F 3 7 the cooler 16 which comprises a supplementary cooling A1203 0 38 zone. It may be sprayed in, for example, on a batch or S03 1 6 continuous basis through line 17. This phosphoric acid CO2 5 65 used for cooling and beneticiating the rock is usually in 40 F6203 0 7() the range of 60 to 180 F. Air may also be pumped into sioz 3 0 cooler 16 through line 18. Hot phosphoric acid liquid oi Cao /12205 ratio of 1 6 vapors with impurities or condensate may be removed from cooler 16 through line 19 to a conventional scrubber Tins phosphate rock was Categ m .a uldlzef bed calciner at a temperature of 1450 F. in a continuous and the upgraded rock at a temperature usually in the o process where residence time was essentially one hour range of 250 to 400 F. may be removed through line 20.

after which the phosphate rock was withdrawn from the FIG. 2 illustrates anothei embodiment of the invention air cooling zone at a temperature of approximately where the above described phosphoric acid 1s added to 1000., F

and cooled in a rotary coolei by spraying in phosphate rock particles that are drying at a temperature o 15 pounds of 30 percent phosphoric acid per 100 pounds m the range of 200 to 500 F" more preferably at a tem' of rock at 100 F to reduce the tem erature of the rock perature in the range of 300 to 400 F. It is also preferred p o taken fiom the cooler to approximately 550 F. The that the phosphoric acid be added after any water present phosphate rock removed from the cooler had a CaO/ in the rock particles is evaporated. Phosphate feed rock P O ratio of a roximater 1 4 (P O a roxmatel particles are fed into dryer 36, that may be a iluid bed or 3 2; gement) pp y 2 5 pp y other convenuolial dryer by hue 3' .Alr and fuel may be An additional number of tests were run using the same fed in through lines 7 and 8 respectively. Water vapor or t e of three sta e calciner wherein a 27 ement hos steam may be removed from dryer 16 through line 17 and yp g p p phos horic acid may be added through liiie 18 Cooled phone acld Was.used to C001 10.0 grams of a phosphate p rock feed material of the following weight percent comand beneciated phosphate rock may be removed through Ositio Percent line 15 and any liquid acid or residue may be removed 60 ao 48 3 through line 20. P O 30`6 When a multiple stage uid bed calciner is used to prac- Rzatio Of/P--Ss tice this invention a small quantity of the aforesaid phos- 2 5 phoric acid, particularly a 30 percent acid may be added The pertinent data and results of these tests are set to the upper zone of the calciner in a quantity varying forth in the following table:

TABLE I Dgltention Product 1 Temperature Grams Cldieiililg Weight Percent Maintained Grams P205 in Step Ratio During Cooling Acid Acid (minutes) CaO P205 Cao/P205 220 F i5 4. 0 30 40. 7 35. 0 1. 40 220 F i0 2. 7 30 50. 6 34.9 1. 45 220e F 5 i. 3 30 51.0 34. 0 1.50 550 F 15 4. 0 60 40.1 35. 0 1.4i 550 F 10 2. 7 00 50. 0 34. 0 1.45 550 F 5 1. 3 60 51. 0 34. 0 1.47

What is claimed is:

1. A method for beneticiating phosphate rock having a C210/P205 ratio in excess of 1.50 in a fluidized bed wherein the rock moves countercurrent to the uprising tluidizing gases comprising establishing a plurality of superposed fluidized` bed treatment zones including an upper preheating zone, an intermediate calcination zone and a lower cooling zone, feeding comminuted phosphate rock having a particle size in the range of from -200 to +200 Tyler mesh to said upper preheat zone to provide a bed therein, supplying fuel to said bed, preheating said phosphate rock bed to a temperature in the range of about 200 to 1200 F. by burning said fuel in the presence of air passing upwardly through said bed to lluidize the same, transferring the thus preheated rock by gravity overflow from said fluidized bed in the upper preheating zone to said calcination zone, forming a bed therein of preheated phosphate rock, calcining said phosphate rock in said calcination zone at a temperature in the range of about 1200 to 1850 F. for a period ranging from about minutes to 2 hours by the combustion of fuel supplied to said calcining bed in the presence of preheated air passing from the cooling zone upwardly through said calcining bed to tluidize the same; transferring hot calcined rock from said calcination zone to said cooling zone by gravity overow, to form a bed of calcined phosphate rock in the latter zone, cooling said rock to a temperature of from about 600 to 1200 F. with relatively cool air at ambient temperature, said air being preheated by passing upwardly through said cooling zone bed, said preheated air then passing upwardly through said calcining zone bed to thereby fluidize the cooling zone bed and the calcining zone bed as aforesaid, withdrawing the relatively cooled calcined phosphate rock from said cooling zone to a supplementary cooling zone, adding phosphoric acid at a temperature in the range of about 60 to 180 F., said acid having a P205 content `from about 20 to `40% by weight, to said withdrawn calcined rock in amounts sufficient to cool said calcined rock in the supplementary cooling zone to a temperature of from about 220 to 550 F., thereby simultaneously beneciating said rock by increasing its BPL content and lowering its Cao/P205 ratio to a level below 1.50.

2. The method of claim 1 wherein from 2 to 20 pounds of phosphoric acid are added per 100 pounds of calcined rock.

3. The method of claim 1 wherein the phosphate rock contains sulphide sulphur, and about l to 5 pounds of phosphoric acid of 30% concentration is added per 100 pounds of phosphate rock, to the upper preheat zone to reduce the sulphide sulphur in the final calcined product.

4. The method of claim 1 wherein the phosphate rock BPL content is within the range of 66 to 70% and suicient phosphoric acid is added to the withdrawn calcned phosphate rock to raise the BPL content of the final calcined rock product to a value of at least References Cited UNITED STATES PATENTS 1,706,101 3/1929 Blumcnberg 71-33 XR 1,910,617 5/1933 Leu 71-41 2,442,969 6/1948 Butt 71-41 XR 3,364,008 1/1968 Hollingsworth et al. 71-41 3,376,124 4/1968 Hollingsworth 71-41 XR 3,389,959 6/1968 Lee 71-33 XR REUBEN FRIEDMAN, Primary Examiner B. H. LEVENSON, Assistant Examiner U.S. Cl. XR. 75ml 

